It is known to form "Z-folding" envelopes from a web in which each envelope length in the web is divided into three substantially equal parts by two fold lines. These parts are defined arbitrarily as the anterior, central and posterior parts of the envelope. On the web surfaces may be printed information on the anterior, central and posterior parts of each envelope length. For example, address information may be printed on the anterior part of the envelope.
After the web is cut, each envelope length is Z-folded such that the printed surfaces of the central and the posterior parts are in face-to-face contact. The anterior part is folded over the central part in an opposite direction to the posterior part such that the non-printed surfaces of the posterior and central parts are in face-to-face contact.
The Z-folded envelope is sealed together with adhesives applied to the web surfaces. The contacting surfaces of the envelope parts have adhesives arranged along transverse and longitudinal lines. For example, these adhesives are positioned on the printed surfaces of the posterior and central parts, and on the non-printed surface of the anterior and central parts of the envelope length. The envelope webs may be delivered and stored either as a web roll or packets of a web folded in a zigzag configuration along the transverse cutting lines of the envelope lengths. When the web is folded and stored in a zigzag pattern, the printed envelope surfaces (or surfaces to receive printing) of two successive envelope lengths are folded so as to be face-to-face and, alternatively, the non-printed surfaces of two other envelope lengths are folded into face-to-face contact. Thus, each surface of an envelope length with its associated adhesive strips is face-to-face with its counter-part surface of an adjacent envelope length.
French Patent Application FR-A-2,431,964, describes a process for preventing the adhesive strips on the envelope lengths from adhering to the adhesive facing strips on adjacent envelope lengths during storage of web packets. This process consists of transversely offsetting parts of each longitudinal adhesion line with respect to another part of the same line on an adjacent envelope surface. However, in the process described in FR-A-2,431,964, the transverse lines of adhesives on the envelope lengths are not modified.
Web rolls of envelopes also have problems with adhesive strips bonding together during storage. However, the problem in a roll manifests itself differently than in a folded web packet, because in a roll the printed surface on one envelope comes into contact with the opposite surface of another envelope in the web. In a web roll, the relative orientation of the lines of adhesive on adjacent turns of the web roll varies from one turn of the roll to another. Accordingly, the process described in FR-A-2,431,964 is not applicable to web rolls.
It is the aim of the present invention to solve the problem of bonding between adhesive strips that come into contact during storage of a web of Z-folding envelope lengths. The present invention is intended to be applicable to web rolls and folded web packets.
The invention provides a web of envelope lengths each having front and back surfaces. The web may be cut into individual envelope lengths where each envelope may have two adhesive longitudinal edge strips and transverse adhesive strip(s) on the front and back surfaces of the web. The adhesive strips have the following features: (1) all of the transverse adhesion lines are constituted by adhesion spots spaced apart from one another, and (2) the areas of adhesive of the front web surface are contained in a first longitudinal zone of the web, and the areas of adhesive on the back surface are contained in a second longitudinal zone of the web, the first longitudinal zone(s) being outside the second longitudinal zone(s) and vice versa.
Since the areas of adhesive on one surface of the envelope lengths are in a different longitudinal zone(s) from the longitudinal zone(s) which contains the areas of adhesive of the opposite surface, the adhesive areas do not overlap when the web is in a roll. Thus, there is no bonding between adjacent adhesive areas during storage of the web roll. Similarly, when the web is folded into a packet and individual envelope lengths are folded front surface against front surface and back surface against back surface, it is possible to avoid overlapping adhesive areas by segregating the areas of adhesive appropriately in the separate longitudinal zones described above.
In the present invention, the longitudinal adhesive zones of the front surface and the longitudinal adhesive zones of the back surface may be adjacent or separated by neutral zones which have no adhesive on the front or back zone surfaces. Usually, edges of the web will constitute neutral zones as they may possibly contain drive perforations for a tractor web feeder.